I'm afraid that did not help me. (call me dense)
What does pre-wired mean...is the woof in the wall, or outside the wall.
Is the woof plugged in to the wall near the sofa.
The wire that feeds signal to the woof...does the woof have an RCA jack on the back of it..and that is the wire you are talking about?
Is the wire you are trying to use a shielded one, or a parallel zip of the 24 guage variety?
The signal wire to the woof has to have shield to shield, so the signal has a hot and a ground wire. Mix then up, you get hum..Identify the "hot" one by touching it only, with the woof on, but at a low level. the hot causes hum when you touch it..that is the center of the rca.
I am sorry for all the dumb questions, but you have not given me much to go by, so I am guessing.
Cheers, John